Can training a model on a dataset composed by real images and drawings hurt the training process of a real-world application model?
To my knowledge the deployment model (that you will test on underwater images) as inference will not have a negative effect. Yet drawings may even help differentiate some classes at training and inference. Provided that you won't use drawings in inference, adding them in training phase will not necessarily hurt the accuracy. Note that a drawing of a particular class should not be in the search domains of other classes, namely, a drawing of a particular class should not be the same with the other classes.